This invention relates to a fluid displacement apparatus, and more particularly, to a fluid compressor or pump of the type which utilizes an orbiting fluid displacement member.
Several types of fluid displacement apparatus are known which utilize an orbiting fluid displacement member driven by a Scotch yoke type shaft coupled to an end surface of the fluid displacement member. One such apparatus, which is disclosed in U.S. Pat. No. 1,906,142 issued to John Ekelof, is a rotary machine provided with an annular and eccentrically movable piston adapted to act within an annular cylinder with a radial transverse wall. One end of the wall of the cylinder is fixedly mounted and the other wall consists of a cover disc connected to the annular piston. The piston is driven by a crank shaft. Another prior art apparatus, which is shown in U.S. Pat. No. 801,182, issued to Creux, utilizes orbiting and fixed scrolls as the fluid displacement members.
Though the present invention applies to either a piston type or scroll type of fluid displacement apparatus, i.e., using either a movable annular piston or an orbiting scroll, the description which follows will be limited to a scroll type compressor. The term fluid displacement member is used generically to describe a movable member of any suitable configuration in a fluid displacement apparatus.
The scroll type apparatus shown in the Creux patent, U.S. Pat. No. 801,182, includes two scroll members each having an end plate and a spiroidal or involute spiral element. These scroll members are maintained angularly and radially offset so that both spiral elements interfit to make a plurality of line contacts between their spiral curved surfaces to seal off and define at least one pair of fluid pockets. The relative orbital motion of the scroll members shifts the line contacts along the spiral curved surfaces so that the fluid pockets change in volume. The volume of the fluid pockets increases or decreases dependent on the direction of the orbital motion. Thereof, this scroll type fluid apparatus is applicable to compress, expand or pump fluids.
Typically, in a scroll type apparatus, a drive shaft receives and transmits a rotary driving force from an external power source. The drive shaft is rotatably supported by a bearing disposed within a housing. In particular, as shown in U.S. Pat. No. 3,874,327, the drive shaft is rotatably supported by two bearings disposed within the housing.
Referring now to FIG. 1, a prior art shaft support construction will be described. Drive shaft 13', which includes a disk shaped rotor 131' at its inner end portion, is rotatably supported by first bearing 19' disposed within sleeve 17' projecting from front end plate 11'. Disk shaped rotor 131' also is rotatably supported by second bearing 16' disposed within opening 111' of front end plate 11'. A crank pin or drive pin axially projects from an end surface of disk shaped rotor 131', and is radially offset from the center of drive shaft 13'. The drive pin is connected to an orbiting scroll for transmitting orbital motion from drive shaft 13' to the orbiting scroll. The orbiting scroll is coupled to a rotation preventing device so that the orbiting scroll undergoes orbital motion upon rotation of drive shaft 13'.
Scroll type fluid displacement apparatus of the above type is suited for use as a refrigerant compressor of an automobile air conditioner. Generally, the compressor is coupled to an electromagnetic clutch for transmitting the output of the engine to the drive shaft of the compressor. The magnetic clutch comprises a pulley 22', magnetic coil 23' and armature plate 24'. Pulley 22', which is usually rotated by the output of the engine, is rotatably supported by sleeve 17' through bearing 21' disposed on the outer surface of sleeve 17'. Magnetic coil 23' is mounted on the outer surface of sleeve 17' by a support plate and armature plate 24' is elastically supported on the outer end portion of drive shaft 13'.
In the construction shown in FIG. 1, drive shaft 13' and disk shaped rotor 131' are generally supported by two bearings 16' and 19' which are axially spaced. Since bearing 16' is placed on front end plate 11' at a position which is axially spaced from the driving point of the orbiting scroll, bearing 16' carries a great load during orbital motion of the orbiting scroll. The other support bearing 19' is positioned inside sleeve 17' so that the diameter of sleeve 17' must be enlarged, which in turn increases the outer diameter of the magnetic clutch which is disposed on the outer surface of sleeve 17'. Furthermore, because sleeve 17' extends from an end surface of front end plate 11', it must be cantilevered, which requires a sleeve with considerable mechanical strength. Also, because the tensile force of the belt is transmitted to sleeve 17' through pulley 22' and bearing 21', the thickness of sleeve 17' must be limited so that the diameter of bearing 21' which supports the pulley 22' cannot be decreased. These physical constraints result in a larger outside diameter of the compressor itself.
Furthermore, scroll type compressors usually are provided with first balance weights to cancel the centrifugal force due to the orbital motion of the orbiting scroll and other balance weights to cancel the moment which arises from the operation of the first balance weights. Therefore, another physical constraint in designing the compressor is the necessity for arranging these balance weights.